import java.util.Scanner;
class Point{
  double x;
  double y;
  public Point(double x,double y){
    this.x=x;
    this.y=y;
  }
  public static double Distance(Point a,Point b){
    double z;
    z=Math.sqrt(Math.pow((a.x-b.x),2)+Math.pow((a.y-b.y),2));
    return z;
  }
}
public class Main{
  public static void main(String[] args){
    Scanner reader=new Scanner(System.in);
    int x1=reader.nextInt();
    int y1=reader.nextInt();
    int x2=reader.nextInt();
    int y2=reader.nextInt();
    Point p1=new Point(x1,y1);
    Point p2=new Point(x2,y2);
    double a=Point.Distance(p1,p2);
    System.out.printf("%.2f",a);
  }
}